1. Field of the Invention
The present invention relates to a process for producing a styrene polymer composition, more specifically to a process for producing, with a high efficiency, a styrene polymer composition which comprises a styrene polymer having a high degree of syndiotactic configuration in its stereochemical structure of the polymer chain and a rubber-like elastomer, and which has a high dispersibility of rubber component.
2. Description of the Related Arts
Heretofore, styrene polymers produced by the radical polymerization method have an atactic configuration in stereostructure and are molded to various shapes by various molding methods such as injection molding, extrusion molding, blow molding, vacuum molding and cast molding, and they have been widely used as domestic electric appliances, office machines, household goods, packaging containers, toys, furnitures, synthetic papers and other industrial materials.
However, such styrene polymers having atactic configuration have disadvantage that it is inferior in heat resistance and chemical resistance.
The group of the present inventors has previously succeeded in developing styrene polymers having a high degree of syndiotacticity (see Japanese Patent Application Laid-Open Nos. 187708/1987, 179906/1988, 241009/1988, etc.).
Since the styrene polymers having a syndiotactic configuration have melting points which are different from those of the conventional atactic polystyrenes, and are higher than those of the isotactic polystyrenes known before, they are expected to be used as heat-resistant resins in various fields. To utilize the heat-resistance of them with good efficiency, blending them with other resins have been studied (Japanese Patent Application Laid-Open Nos. 257950/1987, 146944/1989, and 279944/1989).
In these studies, by blending these styrene polymers with a rubber-like elastomer, resin compositions having improved impact strength were obtained. In producing the compositions with rubber-like elastomer, however, blending as been effected by kneading, but a sufficient kneading has been required for improving the dispersibility. In that process, since the rubber-like elastomer is provided with elasticity, it must be cut into fine pieces before kneading, but it involved some problems owing to its elasticity.
Because of their high melting points, the styrene polymers having a syndiotactic configuration were kneaded at high temperature, but if shearing force or time for sufficient kneading became excessive, the molecular weight of the resin might be lowered or cross-linking of rubber might proceed.
Under these circumstances, the present inventors have intensively studied to develop a process for producing resin composition having a good dispersibility and a high impact strength, whereby the styrene polymer having a syndiotactic configuration and rubber-like elastomer can be blended efficiently, and the above problems are dissolved.